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- ItemThe Effect of Iron and Vanadium in VOy/Ce1-xFexO2-δ Catalysts in Low-Temperature Selective Catalytic Reduction of NOx by Ammonia(Weinheim : WileyY-VCH Verlag, 2020) Keller, Sonja; Agostini, Giovanni; Antoni, Hendrik; Kreyenschulte, Carsten R.; Atia, Hanan; Rabeah, Jabor; Bentrup, Ursula; Brückner, AngelikaSupported VOy/Ce1-xFexO2-δ catalysts (x=0, 0.5, 0.1, 0.2) and bare supports were prepared and tested in selective catalytic reduction (SCR) of NOx by NH3 between 150 and 300 °C with a GHSV of 70 000 h−1. Iron was found to be beneficial for the activity of the pristine supports, reaching 80 % conversion at 275 °C. When vanadium was additionally introduced into the system, iron was found to be detrimental for NOx-conversion. To derive structure-reactivity relationships, V-free supports and VOy/Ce1-xFexO2-δ catalysts were characterized by XRD, XPS, Raman spectroscopy and TEM. In situ XANES, as well as operando DRIFTS and EPR measurements were performed to study the behavior of the catalysts under reaction conditions. Up to an iron content of x=0.1, a solid Ce1-xFexO2-δ solution was formed. Higher iron contents led to formation of iron oxide agglomerates. These agglomerates, as well as an increased amount of surface oxygen species were found to be responsible for increased NOx-conversion over of pure supports. For V-containing catalysts, an interaction of Fe and V centers could be found. Under reaction conditions, Fe3+ was preferentially reduced instead of V5+, decreasing the catalytic activity of VOy/Ce1-xFexO2-δ. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
- ItemTracing Active Sites in Supported Ni Catalysts during Butene Oligomerization by Operando Spectroscopy under Pressure(Washington, DC : ACS, 2016) Rabeah, Jabor; Radnik, Jörg; Briois, Valérie; Maschmeyer, Dietrich; Stochniol, Guido; Peitz, Stephan; Reeker, Helene; La Fontaine, Camille; Brückner, AngelikaSupported Ni catalysts have been studied during the dimerization of butenes by operando electron paramagnetic resonance (EPR) and in situ X-ray absorption spectroscopy (XAS) at 353 K and up to 16 bar. Single NiI/NiII shuttles were identified as active sites, whereby the conversion of initial NiI to NiII by oxidative addition of butene is obviously faster than the re-reduction of NiII to NiI by reductive elimination of the C8 product, rendering the equilibrium percentage of NiI small. At p ≤ 2 bar, NiI single sites form inactive Ni0 aggregates, while this is suppressed at higher pressure (∼12 bar). A reaction mechanism is proposed.